Process for producing cladded fuel elements



United States Patent 3,344,508 PROCESS FOR PRODUCING CLADDED FUELELEMENTS Jacques Andr Stohr, Bures-sur-Yvette, France, assignor toCommissariat a lEnergie Atomique, Paris, France No Drawing. Filed Jan.20, 1964, Ser. No. 338,621 Claims priority, application France, Feb. 20,1963, 925,479 2 Claims. (Cl. 29-4205) The present invention relates toco-extrusion and corolling processes which are employed in particularfor the purpose of obtaining fuel elements in the form of round bars,tubes or plates.

The invention is more especially concerned, among the aforesaidprocesses, with those which permit the possibility of obtaining saidfuel elements from composite billets or blooms in which the core ofthese latter constitutes the fuel proper whereas the outer portionthereof constitutes the cladding material, and which effect at the sametime the formation of a metallurgical bond between the fuel and the canas well as the shaping of the round bar, tube or plate.

In the processes of the prior art, the co-extrusion or c0- rollingoperation was performed either directly on a composite billet or bloomor alternatively on a composite billet or bloom which was placed withina jacket, the function of which was to ensure that materials to betransformed were protected from the surrounding atmosphere.

The performance of these operations without jacket ing is subject to thedisadvantages which arise from absence of protection, for example thenitriding and corrosion effects which result in the case of zirconium orzirconium alloys. Moreover, the use of conventional protective jacketsof steel increases the cost price of the operation to a considerableextent.

The object of the present invention is to make the said processes suchthat these latter meet the various practical requirements moreeffectively than has hitherto been achieved, especially insofar as theypermit the possibility of overcoming the drawbacks mentioned above byensuring that the shaping operation and provision of a metallurgicalbond are carried into effect in the correct manner without callingeither for protective jacketing, controlled atmosphere preheatingfurnaces or complex apparatus for the purpose of welding or sealingjackets or blooms which had been necessary up to the present time.

The invention mainly consists-after having effected the metallurgicalbond by diffusion between the fuel and the can by means ofthermo-pneumatic or hydrostatic machinein subjecting the productobtained to a plastic state deformation process such as rolling orextrusion, at a temperature which is compatible with the materialsemployed.

Apart from this main arrangement, the present invention further consistsin certain other arrangements which are preferably employed at the sametime and which are to be considered either separately or in combination,namely:

The metallurgical bond between the fuel and the can is ensured, aftersealing of the fuel-can assembly by welding, by maintaining saidassembly at a suitable temperature and pressure during the time which isnecessary to obtain a diffusion bond between the constitutent materials;

Patented Oct. 3, 1957 The aforesaid operation is carried out underhydrostatic pressure (water or oil, for example);

The aforesaid operation is carried out directly on the can-fuel assemblyin a neutral gas atmosphere (argon, for example);

The aforesaid operation is carried out on said assembly which has beenpreviously enclosed within a sealed casing (thin sheet of steel orcopper, for example) which is closed in a vacuum or in an inert gas, andthe atmosphere can in that case be any suitable gas.

The invention will in any case be more clearly understood by perusal ofthe complementary description and of the example which now followsbelow, said complementary description and said example being givensolely by way of indication and not in any sense by Way of impliedlimitation.

The process in accordance with the invention makes it possible toreplace the conventional protective jackets (for example of steel) whichare both of substantial thickness and costly by thin'walled casings (ofsteel or copper sheet, for example). A further economic advantage of theprocess is that its dispenses with the use of furnaces for preheating athigh temperature in a controlled atmosphere as well as the use ofapparatus for welding and sealing jackets. Moreover, the process inaccordance with the invention transforms the operations involvingco-extrusion or co-rolling in a jacket at high temperature intooperations involving co-extrusion or co-rolling without jacket atmoderate temperature.

In the case, for example, of zirconium or its alloys, the fuel-canassembly will be processed within a thermo-pneumatic machine and broughttherein to a temperature of 750 to 950 C. at a pressure of at least 30kilograms per square centimeter and will be maintained therein for aperiod of time which depends on the pressure and temperature adopted.

Uranium-zirconium fuel elements containing 2 to 8% by weight of uraniumand clad with zircalloy have been metallurgically bonded under thefollowing conditions: Temperature, 800 C.; pressure, 300 kgs./cm. time,30 minutes; gas, neutral gas (argon, for example, or air).

The fuel elements were placed, in the case of air, within the protectiveboxes of copper or steel sheet of A mm. thickness.

It was possible to carry out the rolling of said fuel elements in thecold or warm state, that is to say within the range which is comprisedbetween room temperature and 400 C., and within which no nitridingof thezirconium takes place, this result being achieved without the aid of anyprotective expedient. The elements thus rolled have shown no defect inthe zone which was bonded by diffusion as a preliminary step.

It Will be understood that the present invention is not limited in anyrespect either to the mode of application or to the example of executionwhich has been more especially contemplated but is intended, on thecontrary, to include within its scope all alternative forms.

What I claim is:

1. A process for producing a fuel element comprised of a core sectionconstituting the fuel proper and an outer protective cladding for saidcore section, said process comprising the following steps: (a)contacting a uraniumzirconium fuel mixture containing from about 2 to 8%weight uranium with a cladding zircalloy to form a composite; (b)subjecting said composite to a temperature of approximately 800 C., atapproximately 300 kgs./cm. pressure for a time of approximately 30minutes in an inert atmosphere to thereby obtain a metallur-gicallybonded metallic material; and (c) subjecting the material obtained fromstep (b) to a plastic state deformation process at a temperature rangeof from room temperature to 400 C.

2. A process according to claim 1, wherein prior to step (b), thecomposite is enclosed and sealed in an evacuated casing comprised ofmetal sheeting having a thickness of approximately mm.

References Cited UNITED 10 JOHN F. CAMPBELL, Primary Examiner.

CHARLIE MOON, Examiner.

P. M. COHEN, Assistant Examiner.

1. A PROCESS FOR PRODUCING A FUEL ELEMENT COMPRISED OF A CORE SECTIONCONSTITUTING THE FUEL PROPER AND AN OUTER PROTECTIVE CLADDING FOR SAIDCORE SECTION, SAID PROCESS COMPRISING THE FOLLOWING STEPS: (A)CONTACTING A URANIUMZIRCONIUM FUEL MIXTURE CONTAINING FROM ABOUT 2 TO 8%WEIGHT URANIUM WITH A CLADDING ZIRCALLOY TO FORM A COMPOSITE; (B)SUBJECTING SAID COMPOSITE TO A TEMPERATURE OF APPROXIMATELY 800*C., ATAPPROXIMATELY 300 KGS./CM.2 PRESSURE FOR A TIME OF APPROXIMATELY 30MINUTES IN AN INERT ATMOSPHERE TO THEREBY OBTAIN A METALLURGICALLYBONDED METALLIC MATERIAL; AND (C) SUBJECTING THE MATERIAL OBTAINED FROMSTEP (B) TO A PLASTIC STATE DEFORMATION PROCESS AT A TEMPERATURE RANGEOF FROM ROOM TEMPERATURE TO 400*C.